1. Field of the Invention
The present invention relates to an imaging device, and in particular, to an electronic imaging device having a zooming optical system.
2. Description of Related Art
A zooming optical system comprises lens units: a unit varying the focal length (a variator), a unit compensating for the shift of an image surface and aberration resulting therefrom (a compensator), a unit focusing an object, and a fixed unit correcting aberration characteristics.
The zooming optical system is constructed so that the magnification change and focal adjustment thereof are performed by moving a predetermined lens unit, of the above-mentioned lens units, in the coaxial direction.
The mechanical structure for moving these lens units, however, is complicated, and there is the problem that a wide space is necessary for installing this mechanical structure.
Available methods for moving the lens units of a zooming optical system include a manual method of manually moving lenses via a zooming ring as in a single-lens reflex camera, and a motor driving method of moving lenses by driving a motor through the operation of a zooming lever or a button attached to the device.
The manual method, however, has the problem that it is difficult to provide a lens with a collapsible mount, and the lens may remain in a projecting state when the device is not used, this constituting an obstacle to carrying.
The motor driving method, on the other hand, has problems such as a slow zooming operation, noisy operation and large power consumption. In addition, it is necessary to provide a motor and a driving circuit for operating the motor, resulting in oversizing of the device.
Regarding the focusing mechanism of the zooming optical system in the imaging device, automatic focusing forms a main current, and because of the absolute necessity of motor driving, problems such as a slow operation, noisy movement and large power consumption are encountered.
Furthermore, in the case of the motor driving method in which the lens is collapsed during non-operation, the lens must be largely moved at start and end of operation, causing a further increase in power consumption.
There is recently a demand for an imaging device using a compact and high-resolution zooming optical system. For example, Japanese Patent Kokai No. Hei 11-220646 proposes an imaging device using a zooming optical system downsized by folding the optical path. The optical path is merely folded, with power consumption not markedly reduced.